Hot melt inks for inkjet printing are characterized by being solid at ambient temperature and liquid at printer operating temperature. Hot melt inks are advantageous over liquid ink because transportation is easier, solvent evaporation and viscosity changes are of no concern. Hot melt inks provide better print quality and resolution since the inks solidify and dry more quickly without wicking into the substrate.
Thus, solid hot melt inks are loaded in a printer capable of melting the ink in the inkjet printer head, ejecting the liquid ink which quickly resolidifies upon impacting a substrate. Conventional hot melt inkjet printers operate with a printing head and inkjet temperature of about 120 to about 150 C. At those temperatures, the solid ink is melted to a low viscosity liquid, generally about 8 to 25 cP when measured at jetting temperature. To form a three-dimensional solid object, the ink jet operation is repeated over several passes so that an object is formed layer by layer.
Hot melt inks generally comprise colorant inks such as dyes and pigments along with base materials commonly referred to as ink vehicles. Conventional ink vehicles generally include various proportions of resins, plasticizers, tackifiers, viscosity modifiers and antioxidants.
PCT patent application WO 9414902 describes hot melt inks for inkjet printing which comprise colorants and urethane oligomers as ink vehicles and which were obtained by reacting diisocyanate compounds with various aliphatic alcohol.
PCT patent application WO 9712003 describes hot melt inks for inkjet printing which comprise colorants and ink vehicle and which were obtained by reacting a mono- or diisocyanate with one or more functional amide materials.
U.S. Pat. No. 4,889,560 teaches the preparation of hot melt inks comprising colorants and an ink vehicle. The ink vehicle is described as containing fatty mono-amide and tetra-amide compounds. The ratio of tetra-amide to mono-amide varies between 2 to 1 and 1 to 10.
U.S. Pat. No. 5,597,856 teaches the preparation of hot melt inks comprising colorants and an ink vehicle. The ink vehicle is described as containing a mixture of mono-amide, unsaturated amide and tetra-amide compounds.
U.S. Pat. Nos. 5,750,604; 5,780,528; and 5,783,658 teach the preparation of hot melt inks for inkjet printing which comprise colorants and ink vehicles containing urethane-urea and urea-urea compounds.
U.S. Pat. No. 5,902,841 teaches the preparation of hot melt inks comprising colorants and an ink vehicle. The ink vehicle is described as containing hydroxy functional fatty amide compounds.
U.S. Pat. Nos. 5,777,023 and 5,881,648 teach the preparation of hot melt inks comprising colorants and an ink vehicle. The ink vehicle is described as containing diamidediurethane compounds obtained by reacting monoamine and diisocyanate or diamine and isocyanate.
Although meritorious, the hot melt inks for inkjet printing processes taught in the prior art suffer multiple drawbacks and disadvantages once jetted on a substrate, such as poor mechanical properties and tackiness upon touch.
Furthermore, none of the prior art hot melt inks contain silicon-based materials such as the polyhedral silsesquioxanes described in the present invention.
As a result, there remains an important need for new hot melt ink compositions with improved dryness to touch and improved mechanical properties. Also needed are novel hot melt ink jet compositions allowing for post printing treatment processes to further increase mechanical durability, optical density, electrical conductivity and dryness.